The hidden identity of Batman is one of the best-kept secrets in all of DC Comics, but Bruce Wayne has more than paranoia to conceal the man behind the mask. While other masked superheroes like Spider-Man frequently come across individuals who know their secret identity, Batman is fiercely protective of his Bruce Wayne persona, to the point where not even most heroes are aware of the man under the cowl (aside from Superman and the various members of the Bat-Family). Batgirl and the Birds of Prey #5 contains another reason why Gotham City will never even consider that Bruce Wayne is Batman: he's only one person.
Very few people know that Bruce Wayne is Batman, and the vast majority of people on the list were told by Wayne himself. Alfred remains the one person who was informed of Bruce Wayne's plan before he became Batman (in most comic continuities, he worries constantly about Bruce's choice but helps him in his crimefighting endeavors nevertheless). Some villains, like Deathstroke and Hugo Strange, manage to find out on their own (and their knowledge is retained through the New 52 reboot onward). Silver St. Cloud remains the only love interest to figure out Bruce's true identity on her own, thanks to her suspicions and Bruce Wayne being a slightly less protective and paranoid person in the 70s than he is today.
In Batgirl and the Birds of Prey #5, Batgirl and the team meet up with computer hacker Gus, a very brash individual who claims to have information about Batman that no one else knows. Barbara Gordon is clearly nervous, but must play along. "He's not one dude, he's like six guys!" reveals a triumphant Gus. The hacker sees no other way how Batman can appear all over Gotham so quickly, not to mention his exploits with the Justice League. "I'm still working on all the identities, but I'm right, right?" Batgirl can only nod her head and "confirm" Gus' suspicions. Bruce's identity is safe, thanks to an overthinking Gothamite.
This theory has appeared more than once in Batman lore, and is the perfect way to conceal Bruce Wayne's identity. The "Bat-Men" must coordinate their attacks, and the idea that the aloof Bruce Wayne would become one of them, let alone "share" the glory among others, is ludicrous to many Gothamites. Combined with his constant use of the shadows and stealth along with the fact that he rarely appears during daylight means that even Batman's chin is rarely glimpsed by criminals.
Even though Bruce Wayne disappears whenever Batman shows up, most Gothamites rarely assume that a billionaire playboy is secretly Gotham City's most famous crimefighter. Batgirl acquiescing to the rumor that Batman is multiple people even suggests that the Bat-Family is willing to play along with the suspicion. Batman's identity is safe, because Gotham City keeps looking for multiple people, not one.